Development of a DC-DC converter-based balancing system for Lithium-ion battery cells based on State of Power reference

Abstract

In recent years, Li-ion battery packs have become a major component of new technologies like energy storage systems and electric vehicles. Due to the safety limitations inherent to Li-ion battery cells, these packs need to be operated under precise voltage, temperature, and current conditions, which are variables supervised by a BMS. Depending on the application, battery packs are often comprised of several individual cells. However, each battery cell has slight variations, which can lead to performance and service life issues. This problem is addressed by implementing different types of balancing systems. Nevertheless, current methodologies face several limitations, such as a low energy efficiency for passive systems and high costs and complexity for active circuits. A new balancing system, consisting of the combination of a modular active DC-DC converter-based topology, a multi-factor balancing algorithm, and a control strategy for balancing current based on SoP, is developed in this research project. The resulting system can expand the runtime of the battery pack, as the energy is distributed better among cells. Besides, the energy that can be injected into the battery pack during charging has also been increased, as the excess of energy is moved from overcharged cells to the rest before anyone of them reaches its top voltage.